Butterfly valves are in common usage for controlling the flow of various fluid, i.e., liquid or gas, streams. Butterfly valves are used to throttle fluid flow and for on-off applications.
A typical butterfly valve includes a valve body having a passage extending through it and a butterfly valve element pivotally mounted on the valve body. The butterfly valve element is characteristically in the form of a disc.
In certain instances, butterfly valves are used to control the flow of a process fluid which includes particulate and/or other foreign matter. In these instances, the edge of the butterfly valve which faces upstream in the open position is pitted or abraded by the particulates in the fluid stream. When called upon to seal in the closed position, the pitted butterfly valve element can no longer perform its function and leakage occurs through the pitted regions. The size of the leak progressively increases due to erosion, particularly in high velocity particulate-laden applications.
It is suggested in Orton U.S. Pat. No. 1,824,168 to shield the edges of the butterfly valve element utilizing a vane which is aerodynamically shaped and which is narrower than the butterfly valve element. Although the basic concept of shielding the butterfly valve element edge is sound, the narrowness of the vane is undesirable for some applications. Moreover, the vane must be bolted radially through the valve body or through the adjacent fluid-carrying conduits. This increases the likelihood of fluid leakage and complicates installation and removal of the vane.